Sensors, particularly oxygen sensors, are used in a variety of applications that require qualitative and quantitative analysis of gases. In automotive applications, the direct relationship between the oxygen concentration in the exhaust gas and the air-to-fuel ratio of the fuel mixture supplied to the engine allows the oxygen sensor to provide oxygen concentration measurements for determination of optimum combustion conditions, maximization of fuel economy, and the management of exhaust emissions.
A conventional stoichiometric oxygen sensor typically comprises an ionically conductive solid electrolyte material, a porous electrode on the exterior surface of the electrolyte exposed to the exhaust gases with a porous protective overcoat, and an electrode on the interior surface of the sensor exposed to a known oxygen partial pressure. Sensors typically used in automotive applications use a yttria stabilized zirconia based electrochemical galvanic cell with platinum electrodes, which operate in potentiometric mode to detect the relative amounts of oxygen present in the exhaust of an automobile engine. When opposite surfaces of this galvanic cell are exposed to different oxygen partial pressures, an electromotive force is developed between the electrodes on the opposite surfaces of the zirconia wall, according to the Nernst equation:
  E  =            (              RT                  4          ⁢          F                    )        ⁢                  ⁢    In    ⁢                  ⁢          (                        P                      O            2                    ref                          P                      O            2                              )      where:                E=electromotive force        R=universal gas constant        F=Faraday constant        T=absolute temperature of the gas        PO2ref=oxygen partial pressure of the reference gas        PO2=oxygen partial pressure of the exhaust gas        
Due to the large difference in oxygen partial pressure between fuel rich and fuel lean exhaust conditions, the electromotive force (emf) changes sharply at the stoichiometric point, giving rise to the characteristic switching behavior of these sensors. Consequently, these potentiometric oxygen sensors indicate qualitatively whether the engine is operating fuel-rich or fuel-lean, conditions without quantifying the actual air-to-fuel ratio of the exhaust mixture.
Sensors are electrically connected to the vehicle electrical system through the sensor body and wiring harness assembly. At the junction of the sensor and the wiring harness assembly, a seal 106, surrounding the electrical cables, is installed into the retainer 102 of the sensor, as illustrated in prior art FIG. 1. Conventional seals can be comprised of either a one-piece design (seal 106) or be in two parts, a seal 106 and a boot 104, to prevent water and other contaminant intrusion into the sensor 100. Seals comprised of two parts are more effective at preventing contamination, but are more costly. Additionally, during operation of the sensor, volatile hydrocarbons, present in these conventional seals, tend to evaporate at high temperatures, causing the seals to shrink from the walls of the upper shield, or from the cables, allowing contaminants to enter into the sensor.
What is needed in the art is a one-piece seal that prevents fluids, gases and other environmental contaminants from entering the sensor.